The present invention relates to the field of stent delivery systems generally, and more particularly to features for improving stent security on balloon dilatation catheters for use in percutaneous transluminal angioplasty ("PTA") and percutaneous transluminal coronary angioplasty ("PTCA").
In a typical PTCA procedure a guiding catheter having a preformed distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium of the desired coronary artery. A guidewire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to its distal end. The guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses an arterial lesion. Subsequently, the dilatation catheter having an inflatable balloon on its distal portion is advanced into the patient's coronary anatomy over the previously advanced guidewire until the dilation balloon is properly positioned across the lesion. Once properly positioned the balloon is inflated, with radiopaque liquid at high pressure (about 4-6 atmospheres), to expand the arterial passageway.
In a certain percentage of cases, a dilated arterial wall will collapse upon deflation of the dilation balloon or will slowly narrow over a period of time. To solve this problem, after the initial expansion of the artery, the dilatation catheter is removed and a second dilatation catheter equipped with a stent mounted on the dilation balloon is advanced through the guiding catheter and positioned across the arterial lesion. Once in position the balloon is inflated, expanding the stent and implanting it in the arterial wall. The expanded stent is left in place and supports the interior wall of the artery and thereby prevents arterial collapse or narrowing of the artery over time.
Generally, stents are small tubular metallic structures designed for intravascular placement within an artery. A typical stent-delivery system for balloon expandable stents is characterized by a catheter equipped with a dilation balloon and a stent mounted on the balloon. In such a system, the stent is slipped over a folded catheter balloon and crimped in place. A stent crimped onto a catheter balloon is dependant on friction to hold the stent in position and is therefore subject to slippage while being advanced through the patient's vasculature. Occasionally, during advancement, a stent will slide off of a catheter balloon and migrate within a patient's vasculature necessitating emergency removal procedures. This condition most often occurs in small or heavily occluded arteries where contact with either the arterial wall or the lesion to be treated forces the stent off of the catheter balloon. Additionally, sometimes the stent cannot be deployed for a variety of reasons. In these instances, the stent must be able to be pulled back into the guiding catheter without being "stripped off" of the stent-delivery catheter.
What is needed therefore is a catheter with features that provide for improved stent retention. Such stent retention features should serve to prevent contact between a stent and an arterial wall or lesion and should retain the stent on the catheter balloon if such contact does occur. The present invention satisfies these and other needs.